The late actor River Phoenix was briefly reincarnated for cinema audiences on Thursday when his last film finally had its international premiere at the Berlin film festival, 20 years after his sudden death brought an abrupt end to its production.

Phoenix died of a drugs overdose at the age of 23 just 10 days before the completion of Dark Blood, in which he plays a young widower with Native American roots who kidnaps a Hollywood couple.

Dutch-born director George Sluizer rescued the completed rolls of film from the vault of the movie's insurance company, which became the owner of the unfinished material just days before it was due to be destroyed. He finally finished the movie last month, voicing over the scenes from the screenplay that Phoenix never filmed.

His "fundamental idea", he said, had been to "put something together so that the material could be preserved in a proper form, rather than in a wastepaper basket".

"I'm missing about 25% of it, and we lack a number of scenes, but having shown it to a few people after I salvaged it, who raved about the performances, I felt safe enough to continue," he added. Describing it as a "chair with three legs", Sluizer warned the audience in advance that they were about to see an incomplete work. "The fourth leg (of the chair) will always be missing but the chair will be able to stand upright," he said.

Jonathan Pryce, the prolific British film and theatre actor, plays the hoity-toity husband Harry to Judy Davis's Buffy, whose problems begin when their Bentley breaks down during what is supposed to be a romantic weekend in the desert. He said working with Phoenix had been a memorable experience: "I've got only very fond memories of River. We spent six weeks together in Utah, all day and every evening. I found him a remarkable young man and I can't believe looking back that he was only 23 at the time. He was a very old head on young shoulders and was absolutely delightful, very committed and serious."

Pryce said he did not want to touch on the issue of his drug-taking, but the 65-year-old added: "All the weeks we were together in Utah, at no time did I experience him using drugs or abusing drugs in any way, shape or form. I loved him a lot and I love his memory."

But mystery surrounds the whereabouts of some scenes that have never resurfaced but which Sluizer and his cinematographer, Edward Lachmann, are convinced were placed in the vault.

The suspicion is that the scenes may be in the possession of someone who hopes to sell them separately, Sluizer hinted. "The only thing I know is that some rolls have been seen or found in London somewhere. I guess between '93 and '99 some people have been looking at or taking material."

Lachmann said some of the missing footage includes the final ever shots of Phoenix. "Many things around this film were very extraordinary, including the last shot we did of River in this tunnel. We did four takes. After the last take, George said cut … and the lights went down because it was lit from overhead and River became a perfect silhouette and stood there for about 10 seconds. Then he walked up to the camera and his body blocked the lens and it was the most out-of-body experience I've ever had when we watched the film dailies (the unedited footage) the day after he'd passed away," Lachmann said.

"That footage would have been an incredible end to the film," he said.

The film does not have the support of Phoenix's family, who recently issued a statement saying: "Joaquin Phoenix (River's brother) and his family have not been in communication with the director nor will they participate in any way." But Sluizer said he had been in touch with River's mother, saying: "While the family does not participate with the film, the mother of River wished us all the best with the film." Described as an "existentialist latter-day western", the film was warmly received by critics at Berlin, with one calling it a "mystical masterpiece".